1. Field of the Invention
This invention relates to aircraft on-board oxygen generating systems (OBOGS) and to breathable gas delivery regulators of the demand type for use therein.
An OBOGS derives oxygen from the ambient air by passing the air through a molecular sieve oxygen generator system (MSOGS) which delivers breathable gas having a high oxygen concentration for supply through a regulator to a user.
2. Description of the Prior Art
U.S. Pat. No. 4428372 discloses an OBOGS in which a proportion of the breathable gas is also used to charge, through a control valve, an emergency storage tank to dispense with the requirement for the oxygen bottles or liquid store of prior systems. The control valve is controlled by an oxygen partial pressure sensor which allows charging of the emergency tank when the oxygen concentration is between 60 and 95 per cent.
This wide range of oxygen concentration of the stored gas is undesirable firstly, because a user is never certain of the actual concentration of the stored gas at any particular time and secondly because, certainly at the lower end of the range, the concentration would be inadequate for use at high cabin altitudes. Consequently it is desirable that an emergency or back-up breathing gas supply has a concentration of oxygen that is adequate to cater for the worst operational case and should therefore be at least 90 per cent, and which can be guaranteed to be maintained at that level.
There is now also a requirement in the art for a supply of oxygen-enriched breathable gas to be available whilst the aircraft is on the ground either with or without its engines running. Certainly in the latter case the breathable gas has to be drawn from an on-board storage tank and, since in such a case the contents of the storage tank could become significantly depleted, it is essential that recharging is completed as quickly as possible.
The prior art device may not be suitable for such installations firstly because as hereinbefore mentioned the oxygen concentration of the stored gas may not be adequate and, secondly, the charging and control system disclosed in the prior art system may result in an undesirable delay in replenishment of the emergency storage tank.